Question

Possible Duplicate:
Find duplicate records in MySQL

I have a table in MySQL like this:

ID    name    email
1    john     [e-mail]
2    johnny   [e-mail]
3    jim      [e-mail]
4    Michael  [e-mail]

How can I have the MySQL query that will list out the duplicate one like this?

Result of duplicate search:

ID    name    email         Duplicate
1    john     [e-mail]      2
2    johnny   [e-mail]      2

Answer 1

SELECT  a.*, b.totalCount AS Duplicate
FROM    tablename a
        INNER JOIN
        (
            SELECT  email, COUNT(*) totalCount
            FROM    tableName
            GROUP   BY email
        ) b ON a.email = b.email
WHERE   b.totalCount >= 2

• SQLFiddle Demo

for better performance, add an INDEX on column EMail.

OR

SELECT  a.*, b.totalCount AS Duplicate
FROM    tablename a
        INNER JOIN
        (
            SELECT  email, COUNT(*) totalCount
            FROM    tableName
            GROUP   BY email
            HAVING  COUNT(*) >= 2
        ) b ON a.email = b.email

• SQLFiddle Demo